Heater assembly for thermoelectric devices



April 20, 1965 D. J. SCHMITT HEATER ASSEMBLY FOR THERMO-ELECTRIC DEVICESFiled Jan. 17, 1962 INV EN TOR 00/1410 J. Jam/7r United States Patent3,179,911 HEATER ASSEMBLY FOR THERMO- ELECTRIC DEVICES Donald J.Sehmitt, Mansfield, Ohio, assignor to Therm-=0 Disc, Incorporated,Mansfield, Ohio, a corporation of Did Filed Jan. 17, 1962, Ser. No.166,836 3 Claims. (Cl. 338-301) This invention relates generally to athermally operated control device, and more particularly to a heater forsuch device and the method of constructing the same.

In thermo-electric control devices, it has been customary heretofore toprovidea bi-metallic member or assembly upon which a suitable heating orresistance wire is wound or with which the Wire is otherwise associated.Such a bi-metallic assembly is disclosed in my co-pending application,Serial No. 846,725, filed October 15, 1959, now abandoned. In assemblingheating wire about a suitable support which in some cases may consist ofa ceramic, metal'or bi-metallic member or the like, as shown in saidapplication, where it is desired to obtain uniform resistance capacityof a heating wire on the support, considerable trouble has beenexperienced in fixing the first turn of the wire so that it will notbecome displaced from a predetermined or desired position. For thispurpose, a band has been provided. Also cement has been used, and inother cases it has been necessary to weld or braze the wire so as tolocate the leading end of the wire per- 'manently with respect to thesupport. Another drawproduce the desired heating results.

The present invention is directed to a novel bimetallic assembly havinga heating element associated therewith which avoids the variousdisadvantages heretofore noted with respect to the application ofheating wire to supporting structures and which is particularly wellsuited for a valve structure as shown in my co-pending application.

It is among the objects of this invention to provide novel and improvedheaters for thermo-electric devices wherein a uniform wattage eliect maybe produced by such heaters from lengths of heating Wire which may havevarying resistance values.

It is another object of the invention to provide a method of applyingheating wire to a supporting structure Whereby a uniform heat output maybe effected.

A still further object of the invention is to provide a heater assemblyfor thermo-electric controls which is characterized by simplicity andeconomy of construction reliability, efiiciency and uniformity ofoperation and ability to actuate the control within predetermineduniform limits.

These and other objects and advantageous features of j the invention,not at this time more particularly pointed out, will become apparent asthe nature of the invention is better understood from the followingdetailed description, taken in conjunction with the accompanyingdrawing, wherein like reference characters denote corresponding parts,and wherein,

FIGURE 1 isa vertical sectional view taken through a gas valve embodyingthe improved heating element of the subject invention,

FIGURE 2 is a side elevational view taken through a gas valve embodyingthe improved heating element of the subject invention,

FIGURE 2 is a side elevational view partly in section of a heatingelement and bimetal assembly constructed in accordance with the presentinvention,

FIGURE 3 is a front detail view of the bimetal element shown in FIGURE2,

FIGURE 4 is a sectional view taken on the line 4-4 of FIGURE 3,

FIGURE 5 is a perspective view illustrating the first step in windingthe heating Wire upon the bimetal support,

FIGURE 6 is a perspective view illustrating the completion of thewinding of the heating wire on the bimetal element, and

FIGURE 7 is a perspective view showing the completed heater elementready for assembly in the valve of FIGURE 1.

With reference to the accompanying drawing, there is illustrated athcrmo-electrically operated valve for controlling the flow of gas to agas burner made in accordance with the invention disclosed in myco-pending application, Serial No. 846,725, and including a body orhousing generally indicated by the reference numeral Iii. This valvehousing is suitably constructed from a piece of hexagonal stock, such asbrass. The lower end of the valve housing is of reduced diameter and isexternally threaded as at 11 to receive a coupling nut (not shown) forattachment to a gas outlet line. A gas outlet passage 12 is formed inthe reduced end of the body of the valve.

At the juncture between the main portion of the valve housing 19 and itsexternally threaded reduced diameter lower end 11, there is formed ahorizontally inwardly extending annular wall 13 upon which an annularvalve seat 14 is positioned. The valve seat 14 embodies an annular ring15 which is adapted to seat on the annular wall 13 and surrounds anopening serving as a passageway from the interior of the housing 10 tothe outlet 12. Overlying member 15 is a ring shaped member 16, formed ofa suitable rubber-like material having a depending annular wall portion17 which provides a seat to be engaged by a ball type, or other suitablevalve member 18. Above the annular wall 13 the body portion of the valvehousing iii defines a cylindrical gas chamber 19. The upper end of thewall portion is threaded as at 20 to receive a threaded plug 21. Theplug is formed with an axial passage 22 which communicates with theupper end of the gas chamber 19 for delivering gas into the chamber. Theend of the plug 21 is externally threaded to receive a coupling nut (notshown) for connecting this end of the valve to a gas line leading from asuitable source of gas supply.

The spherical ball 18 constitutes the actuating valve member of thevalve and has a diameter slightly larger than the opening through theportion 17 of the valve seat 14. Normally the ball 18 seats by gravityon the valve seat 14 to close the outlet passage 12 from the gas chamber19.

In accordance with the present invention, there is provided a novelthermo-electrically operated assembly for controlling the position ofthe ball 13 with respect to the valve seat portion 17. Referring toFIGURE 2 of the drawings, this thermo-electrically operated assemblyincludes a first bi-metallic member generally indicated by the number 23and includes a mounting segment 24 which is arranged to be secured tothe inside Wall surface of the valve housing 10 by means of a rivet 25adjacent to the upper end of the valve gas chamber 19. This bi-metallicmember 23 also has a horizontal segment 26 which is joined integrally tothe mounting end 2.4 and extends there- 3 p from inwardly toward thelongitudinal center line of the gas chamber 19. At its inner end thisinwardly extending segment 26 is bent at right angles to form anelongated segment27 which extends downwardly at a location approximatelymidway between the wall surface of the gas chamber and the center lineof the chamber and is adapted to serve as a support for the heating wire28.

In assembling the heating wire 23 on the elongated downwardly extendingsegment 27 of the bi-metallic member 23, a layer of insulating tape 29,preferably Fiberglas, is wound around the segment 27. As shown in FIG-URES and 6 the length of tape used is sufficient to provide anoverlapping portion on the face of the segment 27. The leading end ofthe heating wire 28 is formed into a V shaped portion 30 as shown inFIGURE 5 with the free end 31 thereof leading to the terminal connectionof the source of current and the other end 32 projecting parallel withthe overlapped portion of the insulating tape Fiberglas and continuingthereabout for sevcral'convolutions, and then bent downwardly along thebase of the member 23 and secured therebelow.

In the bi-metallic member 23, the arrangement of the metals which havedifferent coefficients of expansion is such that when the elongated leg27 thereof is heated, its

lower end moves laterally inward away from the inner 'wall surface ofthe housing toward the center line of the gas chamber 19. In theoperation of the present valve, the heat which produces such movement ofthe bimetallic member is furnished by thewattage dissipated by theheating wire ZS'surrounding the same.

In accordance with the present invention, a second bimetallic member,designated generally by the reference character 34, is attached to thebase of the movable lower end of the first bi-metallic member 23. Asbest shown in FIGURES 2 and 7, this second bi-metallic member is formedwith a segment 35 at its upper end which is welded to the lower endof'the depending leg 27 of the first bimetallic member. The end of theheating wire 28 is secured between the abutting surfaces of the segments35 and 27 of the respective members. The second bi-metallic member 34 atits lower end is formed with an inwardly protruding horizontal foot 37,which faces toward the ball 18 at a location well below the center ofgravity of the ball.

The arrangement of the metals which make up the second bi-metallicmember 34, which metals have different heat expansion characteristics,is such that when this bi metallic member is subjected .to heat itslower end tends to move counterclockwise, or outwardly away from thecenter line of the gas chamber 19. Thus, the second bimetallic member34.has an opposite direction of movement from the first bi-metallicmember 23 when subjected to-heat.

The heat transfer relationship between the heating wire 28 and thesecond bi-metallic member 34 is greatly reduced from the heat transferrelationship between the heating wire and the first bi-metallic member23 on which it is supported. Accordingly, when the heating wire carriescurrent it has an appreciable heating effect on the first bi-metallicmember 23, but only a negligible effect on the second bi-metallic member34.

The upper end 31 of the heating wire 28 (FIGURE 1) is secured to one endof a flat, flexible metal strip 36. The opposite end of this strip issecured to a rivet 38 which extends through the side wall of the valvehousing 10, opposite the wall on which the bi-metallic member 23 ismounted. The outer end of this rivet is connected to a terminal 40,which may be connected to an external electric circuit in any suitablemanner. An additional rivet 41 is provided for clamping the lower end ofthe terminal against the valve housing 10. A flat strip of suitableelectrical insulating material 42 is engaged between the outside wall ofthe valve housing and the vertically extending leg 40a of the terminal.A smaller strip 43 of the same insulating material is engaged betweenthe inner face of the wall of the valve housing and the mounted end ofthe strip 36. An O-ring 45 of suitable resilient insulation materialextends around the shank of rivet 38 at the opening in the valve housingthrough which the rivet extends. When the rivetis drawn up tight thisO-ring 45 is flattened between the insulation strips .42 and 43 toprovide an effective gas type seal around the rivet 38 as well as toinsulate the rivet 38 from the housing 10.

As previously noted, the resistance of the heating wire is not alwaysuniform, but may vary from time to time in uniform lengths of wire ofsubstantially thesame diameter, thus the amount of heat induced into thesup porting bimetal member from such wire will vary. 7 Such conditionwould cause non-uniformity in the operation of the thermo-electricdevice. It is important therefore to provide a method of assembling theheating wire on its bi-metallic supporting member to obtain a uniformamount of heat input, for only under such conditions will the bimetalassembly be effective to activate the thermoelectric device within apredetermined period of time following the initiation of the flow ofcurrent to the heating wire.

As will be apparent from the foregoing description there is provided amethod of assembling heating wire upon a support which is effective toproduce apredetermined or desired amount of heat. In assembling thelength of wire on the support, the number of convolutions of the wireabout the support is determined as well as the length of wire leadingfrom the first convolution on the support to the terminal. The remainingportion of the wire which is required to produce'the desired amount ofheat is incorporated in the V-shaped portion 30 disposed below theoverlapped portion of the insulating tape. The V-shaped portion can bevaried to compensate for different lengths of heating wire. By priorcheckingthe different lengths of wire for their wattage characteristics,it is possible to provide means for developing a uniform heatapplication in the production of a quantity of the devices described,thus enabling a standardization of performance in any series of devicesintended for identical.

scope of my invention as defined by the appended claims.

I claim: 1. In a thermo-electric control, a bi-metallic heater assemblytherefore comprising a bi-metallic member, in-

sulating means surrounding said bi-metallic member and having anoverlapping portion, a length of heating wire adapted to supply apredetermined amount of heat to the bimetallic memberhaving one endsecured to the. terminal of a source of electric current and the otherend attached to said bi-metallic member, a portion of said heating wireencircling the insulating means in a series of convolutions, a secondportion of said wire intermediate the first convolution and theterminal, being diSPosed within the overlapped portion of saidinsulating means to provide means for readily adjusting the length ofsaid heating wire and to provide a positive attachment to saidbi-metallic member for the leading end of the first convolution of saidheating wire. a

2. In a thermo-electric control, a bi-metallic heater assembly thereforecomprising a bi-metallic member, insulating means surrounding saidbi-metallic member and having an over lapping portion, a predeterminedlength of heating wire adapted to supply a uniform amount of heat tosaid bi-metallic member having one end secured to the terminal of asource of electric current. and theother end attached to saidbi-metallic member, a first portion of said heating wire encircling theinsulating means in a series sulating means to provide means for readilyadjusting the length of said heating wire and to provide a positiveattachment for the leading end of the first convolution.

3. In a thermo-electric control, a bi-metallic heater assembly thereforecomprising a bi-metallic member, insulating means surrounding saidbi-metallic member and having an overlapping portion, heating Wireadapted to supply heat to said bi-mctallic member having one end leadingfrom the terminal of a source of electric current and the other endattached to said bi-metallic member, a portion of said heating wireencircling the insulating means in a series of convolutions, a secondportion of said Wire intermediate the first convolution and the terminalbeing disposed within the overlapped portion of said insulating means toprovide means for varying the length 15 d of Wire within the overlappedportion of the insulating means to effect a uniform heating of thebi-metallic member in a predetermined period of time.

References Cited by the Examiner UNITED STATES PATENTS 2,077,735 4/37Beckler 251-11 X 2,731,230 1/56 Schell 251-11 2,743,574 5/56 McCorkle60-23 10 3,073,938 1/63 Turner et al 200 122 X RICHARD M. WOOD, PrimaryExaminer. ISADOR WEIL, Examiner.

1. IN A THEMO-ELECTRIC CONTROL, A BI-METALLIC HEATER ASSEMBLY THEREFORECOMPRISING A BI-METALLIC MEMBER, INSULATING MEANS SURROUNDING SAIDBI-METALLIC MEMBER AND HAVING AN OVERLAPPING PORTION, A LENGTH OFHEATING WIRE ADAPTED TO SUPPLY A PREDETERMINED AMOUNT OF HEAT TO THEBI-METALLIC MEMBER HAVING ONE END SECURED TO THE TERMINAL OF A SOURCE OFELECTRIC CURRENT AND THE OTHER END ATTACHED TO SAID BI-METALLIC MEMBER,A PORTION OF SAID HEATING WIRE ENCIRCLING THE INSULATING MEANS IN ASERIES OF